You will be required to install the Substratum Theme Engine and have root access OR the Andromeda add-on if you want to apply this theme:

https://play.google.com/store/apps/details?id=projekt.substratum

https://play.google.com/store/apps/details?id=projekt.andromeda

An overlay that enables Always On Display modes for devices running Android 8.1 Oreo and above.

For more details on this modification:
https://www.xda-developers.com/enable-google-pixel-2-always-on-display-on-nexus-6p-pixel-xl/

Known Issues (as of 12/09/2017):
• Waking the screen using the power button or double-tap can be wonky and will get you stuck on a black screen. Can get yourself out the black screen by the locking the screen and using the fingerprint to unlock the device.

This theme is 100% open-source
• https://github.com/InFlames03/Pixel-Enabler

Contact for support suggestions and whatnot:
• Substratum Telegram: t.me/Substratum
• Telegram Group: t.me/SaiThemes
• Telegram PM: t.me/BakaBakaBaka